There will be an emergence of digital signal processing (DSP) based optical transceivers for use in optical transmission systems. Such DSP based transceivers offer great advantages over traditional approaches; this includes: lower costs; smaller size; and increased sensitivity, increased transmission distance, increased transmission capacity, and simpler design, installation, turn-up, and maintenance.
DSP based transceivers can be direct detection or coherent detection based. Direct detection systems come in a variety of modulation formats and include On/Off Keying, Differential Phase Shift Keying and these transceiver systems can use DSP based Maximum Likely Hood Sequence Estimators (MSLE) or other techniques to improve performance. Coherent systems include a variety of modulation formats such as Dual-Polarization Quadrature Phase Shift Keying (DP-QPSK), Quadrature Amplitude Modulation (QAM), and Optical Frequency Division Multiplexing (OFDM). Such coherent DSP based systems can operate over a wide variety of system deployment scenarios including the local area network (LAN), metro, regional, long-haul, and ultra-long-haul applications.
To design an optical transceiver module often requires the development of a complex and costly ASIC or FPGA. ASICs can cost upwards of $1M to develop and can take years of development time. The requirements of the optical transceiver module in general and ASIC in particular are very dependent on the deployment scenario. For example, the chromatic dispersion requirements that the transceiver must operate under in the LAN environment are very different than those found in the ultra-long haul environment. The requirements for these two systems can differ by factors of over 1000. The polarization mode dispersion requirement for a long-haul system running over a legacy fiber that was constructed long ago is very different to the requirements for a long-haul system that is running over a newly manufactured and installed fiber. Finally, the power dissipation desired for the LAN environment (which should be low power) can be very different than that desired or acceptable for the long-haul environment (which can be higher than the LAN).
The fact that ASICs are complex and costly to design, and that the requirements for the ASIC can vary depending on the application, leads to conflicts and design tradeoffs. One choice is to either design one ASIC that has the ability to work over all deployment scenarios but may have a very high complexity, gate count and, most importantly, high power dissipation; or design several ASICs, each of which is tuned to the deployment scenario (e.g. one for the LAN, another for the metro, another for the regional, etc). The latter approach has the advantage of being customized for the deployment scenario but has the disadvantage of requiring much higher development costs plus the disadvantage that the end customer (e.g. a telecommunications carrier) must purchase, install, inventory, and spare a different product for many different deployment scenarios. A single ASIC that supports multiple deployment scenarios and uses a single software base, will lead to easier support, quicker time to market, and reduce the risk of software bugs and failures in the field. Even for optical transceiver designs that do not employ an ASIC but use alternative technology such as an FPGA or other digital logic there is a need to design the digital logic with much of the same goals as would be used to design an ASIC. This includes enabling the digital logic to work over a wide range of application scenarios and minimize the power dissipation
FIG. 1 shows a conceptual diagram of a fiber optical transmission system known to the prior art with a dense wavelength division multiplex (DWDM) transponder. The example shows a router in Boston connected via a short-reach transponder to a line card on a transport system that transmits via a DWDM transponder on the same line card over a long-haul amplified system to a similar distant terminal in New York. As is known in the art there are several variations of this including one in which the DWDM transponder is on the router line card (instead of the transport system), where the optical fiber link has longer distances (e.g. ultra-long haul) or has no amplifier hubs (e.g. LAN) or is used in a submarine application. Furthermore there are many known variants of the DWDM transponder. For example the DWDM transponder may be in a self contained module, may include Forward Error Correction Coding and framing inside the module or external to it (as shown), or there may not be a self contained module at all in which case the components are distributed throughout one or more line cards. For simplicity going forward this discussion will refer to a transceiver module without loss of generality.
As mentioned earlier, it is highly desirable to have one design that can work over local area network (LAN), metro, regional, long-haul, and ultra-long-haul installations. In the prior art either multiple designs were implemented to optimize the power dissipation and other characteristics within the transponder module or a high complexity and high power consumption design was implemented that could work in all these installation scenarios. The resulting design typically was far from optimal in performance parameters such as power dissipation and other characteristics. Further, configuring a prior art transponder requires manually measuring the link characteristics and tuning the transponder to match the link conditions.
Thus there is a need for an approach that allows a single module design to be configured in-situ such that it can be optimized in its power dissipation and other characteristics for a variety of end customer applications that can vary over several orders of magnitude. Such an approach has many benefits to the end customers (e.g. system vendors and telecommunication operators) including lowering capital costs and operational costs by minimizing the products they need to plan for, buy, support, and maintain. The present invention addresses this need.